The current state-of-the-art for video encoding is the ITU-T H.264/AVC video coding standard. It defines a number of different profiles for different applications, including the Main profile, Baseline profile and others.
There are a number of standards for encoding/decoding images and videos, including H.264/AVC, that use block-based coding processes. In these processes, the image or frame is divided into blocks, typically 4×4 or 8×8, and the blocks are spectrally transformed into coefficients, quantized, and entropy encoded. In many cases, the data being transformed is not the actual pixel data, but is residual data following a prediction operation. Predictions can be intra-frame, i.e. block-to-block within the frame/image, or inter-frame, i.e. between frames (also called motion prediction).
In many cases a video encoded at a certain resolution may need to be “spatially downsampled”, meaning reduced in size to a smaller resolution. This may be needed if the video is to be played back on a smaller video screen. In many cases, rather than provide a playback device with a full-resolution encoded video and have the playback device decode and downsample the video, it is advantageous to perform the downsampling before transmitting the encoded video to the playback device. Even in the absence of transmission cost concerns, it may be too time consuming or taxing upon the processing resources of an end device to have the end device receive, decode and downsample a full-resolution video as opposed to receiving and decoding a downsampled encoded video. Accordingly, transcoders are used to convert encoded full-resolution video into encoded downsampled video.
A problem that arises with transcoders is that they are costly in terms of processing power and time delay because they often employ the complicated rate-distortion optimization associated with encoding in many modern video encoding standards. An advantage of a transcoder, however, is that the transcoder has information available from the decoding of the full-resolution video that might be exploited to improve the speed or quality of the encoding process for the downsampled video.
It would be advantageous to provide for an improved transcoder and methods or processes for transcoding that exploit data from the decoding of a full-resolution video.
Similar reference numerals may have been used in different figures to denote similar components.